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Exam questions · Biology · Human Defences and Immunity

Physical and Chemical Barriers

  • 6 exam questions
  • 19 marks
  • 9 quick checks
  1. 1 State [2 marks]

    State two ways in which the skin protects the body from pathogens.

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    Model answer

    Any two from: it is a physical barrier of dead cells with keratin; it makes sebum which kills bacteria; it has friendly bacteria; scabs seal cuts.

    Mark scheme

    • First — 1 mark
    • Second — 1 mark
  2. 2 Name [2 marks]

    Name the substance in tears that kills bacteria, and the acid in the stomach that kills pathogens.

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    Model answer

    Lysozyme, and hydrochloric acid.

    Mark scheme

    • Lysozyme — 1 mark
    • Hydrochloric acid — 1 mark
  3. 3 Describe [3 marks]

    Describe how mucus and cilia protect the lungs from pathogens.

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    Model answer

    Goblet cells make mucus, which traps pathogens in the air that is breathed in. Cilia on the cells in the lining move the mucus up the airways to the throat. The mucus is then swallowed or coughed out.

    Mark scheme

    • Mucus traps pathogens — 1 mark
    • Cilia move the mucus — 1 mark
    • Swallowed or coughed out — 1 mark
  4. 4 Explain [3 marks]

    Explain how lysozyme helps to protect the eye from infection.

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    Model answer

    Lysozyme is an enzyme in tears. It breaks down the cell walls of bacteria, so the bacteria die. This stops them from growing on the surface of the eye.

    Mark scheme

    • Enzyme in tears — 1 mark
    • Breaks down bacterial cell walls — 1 mark
    • Bacteria are killed — 1 mark
  5. 5 Calculate [3 marks]

    In one year, 15% of non-smokers and 36% of smokers had a chest infection. Calculate how many times more likely a smoker was to have an infection. Suggest one reason.

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    Model answer

    36 ÷ 15 = 2.4 times. Smoke damages the cilia, so mucus and pathogens are not moved out of the lungs.

    Mark scheme

    • 36 divided by 15 — 1 mark
    • 2.4 times — 1 mark
    • Cilia damaged — 1 mark
  6. 6 Explain [6 marks]

    Explain why smokers are more likely than non-smokers to suffer from chest infections.

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    Model answer

    In the airways, goblet cells make mucus that traps pathogens and dust, and cilia on the cells move the mucus up to the throat so that it can be swallowed or coughed out. Chemicals in cigarette smoke paralyse and destroy the cilia. The mucus can no longer be moved, so it builds up in the lungs, together with the pathogens it has trapped. The bacteria can multiply there, which leads to infection such as bronchitis. Smokers also make more mucus, and have to cough to clear it.

    Mark scheme

    • Goblet cells make mucus that traps pathogens — 1 mark
    • Cilia move mucus up — 1 mark
    • Smoke damages the cilia — 1 mark
    • Mucus is not moved — 1 mark
    • Pathogens multiply in the lungs — 1 mark
    • Infection such as bronchitis — 1 mark

Quick check

  1. 1

    What do goblet cells make?

    1. ACilia
    2. BLysozyme
    3. CMucus
    4. DPlatelets
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    C: Mucus

    Goblet cells make mucus, which traps pathogens in the airways.

  2. 2

    What is the function of cilia in the airways?

    1. ATo move the mucus up
    2. BTo make mucus
    3. CTo kill bacteria
    4. DTo absorb oxygen
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    A: To move the mucus up

    Cilia move the mucus with the trapped pathogens up towards the throat.

  3. 3

    What does lysozyme do?

    1. AMakes mucus
    2. BClots blood
    3. CMakes acid
    4. DBreaks down bacterial cell walls
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    D: Breaks down bacterial cell walls

    Lysozyme is an enzyme that breaks down the cell walls of bacteria.

  4. 4

    Which acid in the stomach kills pathogens?

    1. ASulfuric acid
    2. BHydrochloric acid
    3. CNitric acid
    4. DCitric acid
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    B: Hydrochloric acid

    The stomach contains hydrochloric acid, which kills most pathogens.

  5. 5

    How do platelets help to protect the body?

    1. AThey kill bacteria
    2. BThey make antibodies
    3. CThey help to form a scab
    4. DThey make mucus
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    C: They help to form a scab

    Platelets help the blood to clot and form a scab, which seals a wound.

  6. 6

    Which is a physical barrier?

    1. AThe skin
    2. BLysozyme
    3. CHydrochloric acid
    4. DSebum
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    A: The skin

    The skin is a physical barrier, while lysozyme and acid are chemical defences.

  7. 7

    How does smoking increase the risk of lung infections?

    1. AIt makes more lysozyme
    2. BIt increases stomach acid
    3. CIt makes the skin thicker
    4. DIt damages the cilia
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    D: It damages the cilia

    It damages the cilia, so mucus and pathogens stay in the lungs.

  8. 8

    Why are these defences called non-specific?

    1. AThey only work against viruses
    2. BThey work against all pathogens in the same way
    3. CThey only work in the stomach
    4. DThey are not defences
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    B: They work against all pathogens in the same way

    They work in the same way against all pathogens.

  9. 9

    In one study, 8% of non-smokers and 20% of smokers had infections. How many times more likely was a smoker to be infected?

    1. A2.5 times
    2. B12 times
    3. C0.4 times
    4. D160 times
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    A: 2.5 times

    \(20 \div 8 = 2.5\) times.